The broad class of equipment known as mobile machinery includes machines known as dozers (sometimes called "bulldozers") which have a front-mounted blade for moving and removing earth as well as other materials atop or near the earth surfaces. Such dozers are sometimes mounted on rubber tires; however, urging the dozer blade through the earth requires very high forward force and for that reason, crawler-mounted dozers are in wide use.
Such dozers are propelled by tracks (much like a military tank) and are capable of exerting high forward force on the blade. Such force is possible since the tracks bite into and engage the ground. Track-ground engagement is quite satisfactory for dozer operations and it is sometimes said the track and the ground are "geared" to one another much like engaged gear teeth.
Dozers remove earth in much the same way that a wood plane shaves wood, i.e., by passing a blade across the earth surface and "rolling up" a layer of earth. Such dozers are employed for road construction and to "shape" the exposed surface of the earth to some contour. They are also used to urge earth to one side or the other of the dozer's travel path rather than merely to push earth straight ahead.
The dozer operator is able to raise or lower the blade and to "skew" it left or right. It is this latter capability which permits earth to be urged to one side of the other. And the operator can also tilt the blade so that one end is higher than the other.
The operator is also able to orient the blade at a different "pitch" which means the blade can be rotated slightly about a horizontal axis extending across the blade. To put it another way, the orientation of the blade can be changed so that the blade angles slightly upwardly.
Until the advent of the invention, adjustment of blade pitch was done relatively infrequently, largely because it was difficult and time-consuming. But the ability to do so is important at least for the following reasons. In hard earth or other material, the lower blade cutting edge can be positioned closer to vertical to better penetrate such material. On the other hand, when the blade is "laid back," the capacity of such blade to carry soft or loose material is increased.
Manufacturers of dozers provide for blade pitch adjustment in a variety of ways. One way involves removing bolts at an attachment point near the lower rear of the blade and adding or removing shims to change blade pitch. Another way is by extending and retracting hydraulic cylinders to change such pitch. Yet another way involves a swinging link pivotably pinned at one end and having two apertures, either of which can accept a blade pin. Blade pitch is a function of which aperture is selected. It is understood that not all related parts are used in both blade pitch positions and this would present the risk of losing unused parts.
Arrangements involving hydraulic cylinders for pitch adjustment are shown in U.S. Pat. Nos. 4,074,769 (Frisbee) and 3,700,044 (Berg). Yet another arrangement for changing blade pitch is shown in U.S. Pat. No. 4,893,683 (Horsch et al.).
The device in the Frisbee patent includes a plate with several sets of bolt holes. Pitch is changed by removing the bolts, moving the plate until another set of its holes is aligned with the bolt holes and re-installing the bolts. The Berg patent involves an arrangement that includes a control lever that controls two bellcranks which in turn control two valves that transmit fluid to actuators which provide a pivoting and tilting action for the bulldozer blade. The direction of fluid flow is dependant on the position of the bell-cranks which must be maneuvered from the operator's seat. Each bellcrank is returned to a neutral position by a spring mechanism in the valves which also returns the lever to a neutral position. The arrangement of the Horsch et al. patent involves reversing the positions of two bearing plates which are of differing thicknesses.
Still other arrangements are shown in U.S. Pat. Nos. 5,333,697 (Frisbee et al.) and 5,507,352 (Frisbee et al.). Both the '697 and '352 patent includes a flip block mounted on trunnions positioned toward one edge of the block. The block is rotated about 180.degree. on the trunnions to either one of two available positions, each of which "sets" the blade at a different pitch until it is again changed manually.
While these arrangements have been generally satisfactory, some of them are attended by certain disadvantages. For example, in the arrangement involving the installation or removal of shims, the work must be performed near ground level and upon a mechanism which, more likely than not, is caked with dirt. And, of course, the arrangement assumes that the required shims will be readily available when needed--such assumption is not always correct.
While the use of hydraulic cylinders is very convenient for the operator, it is more costly to manufacture (and buy) in that the cylinders, hydraulic plumbing and pitch control valve are all required to be installed on the dozer. The swinging link arrangement is vary difficult for one person to adjust at lest in that it requires aligning a pin with a hole which may require dozer movement simultaneous with link-pin engagement. And special tools may be required to effect pitch change. As to the arrangement of the Frisbee et al. patent, it has been found that the cost to manufacture the flip block is unacceptable.